In so-called redundant protection systems, multiple electronic devices are provided in a protection group. For a 1:N protection scheme, for example, the protection group includes one protection device which protects N working devices. A protection device is normally substantially identical to the working devices which it protects, such that all working device functions are protected.
When a protected working device fails, a protection device takes over all protected functions of the working device. In a common arrangement for communication systems, for instance, communication lines which are normally connected to ports or interfaces on the working device are switched to the protection device. Such switching is traditionally accomplished using analog switching techniques and hardware such as relays, on a line side of the interfaces. For 1:N protection arrangements, multiple relays are required.
This approach may present a problem for multiple-interface devices having high interface densities (e.g., 32 interfaces) because of the number of signals, the spacing of analog signal lines required to meet safety and signal quality specifications, and in the case of 1:N or M:N arrangements, the number of relays required. Where the working and protection devices are circuit cards intended for deployment in an equipment rack, for example, in which device interconnections are provided on a backplane of the equipment rack, available physical space is limited, and may not be sufficient to accommodate appropriately spaced signal lines or multiple relays. Communication equipment such as switches or routers, for example, may include many line cards, each having multiple communication line interfaces.
In addition, relays tend to have high failure rates relative to integrated circuit switching components. Relying on relays to perform protection switching may thus be undesirable, especially if no means exist to verify that a switching operation is successful. As relays are also less deterministic than digital switches, accurate timing for switching operations is also difficult for relay-based protection schemes.
The overall operation of conventional protection arrangements or their subsystems is not typically monitored. For example, connections between a protection device and protected working devices are not checked for correct functioning before a protection switch is performed. If these connections are not functioning properly when a protection switching operation is required, then performing the switching operation will not have the desired effect of bringing a protection device into operation. Therefore, these connections represent a potential point of failure in conventional protection arrangements. Verification that a switching operation was successful may also be desirable.